Grinding machine



p 7, 1943- s. E. SCHROEDER GRINDING MACHINE 1O Sheets-Sheet 1 Filed May 12, 1944 Simon ESc/zro eder Sept. 7, 1948. s. E; SCHROEDER 2,448,551

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Patented Sept. 7, 1948 GRINDING MACHINE Simon E. Schroeder, lllpon, Wla, auignor to Barlow i Beelig Manufacturing Company,

Bipon, Win. a corporation of Delaware Application May 12, 1944, Serial No. 585,839 58 Claims. (01. 51-95) The invention relates generally to grinding machines and more particularly to.a machine for grinding cylindrical surfaces.

The general object of the invention is to provide a novel grinding machine for grinding cylindrical or tapered surfaces, which is capable of grinding such surfaces to very close limits.

Another object of the invention is to provide a grinding machine in which the relative feedins movement between the work and the grinding wheel is controlled by a means movable through a large distance relative to the actual feeding movement, thereby permitting'very accurate control of the feeding movement.

It is also an object to provide a novel grinding machine which is automatic to the extent that when a workpiece is placed in the machine and the machine is manually started, the machine will automatically continue the operation and stop when the grinding operation has been completed and the work moved to a position convenient for removal.

Still another object is to provide a grinding machine for grinding peripheral surfaces of workpieces in which the rate of relative feed between the work and the grinding wheel gradually decreases as the work approaches its final dimension.

A. still furtheroblect is to provide a grinding machine for grinding peripheral surfaces of workpieces, in which the workis swung from a loading position to a grinding position and in which the feeding movement of the work toward the grinding wheel constitutes a continuation of such swinging movement.

Another object is to provide a grinding machine for grinding peripheral work surfaces in which the relative feeding movement between the work and the grinding wheel is accomplished by a swinging movement of the work, and'in which the work-is reciprocated parallel to the axis of the grinding wheel during such feeding movement in the same bearings that support the work for the swinging movement.

A still further obiectis to provide a grinding machine in which the grinding wheel spindle must be operating properly, that is. without overheating, the machine being automatically shut down in case such overheating occurs.

Still another object is 'to provide a grinding machine for grinding peripheral surfaces of workpieces, which is provided with means and mechanisms for accomplishing various movements of the parts of the'machine including swinging of the work to the grinding position,

machine of the general character set forth in the preceding object, which is fully adjustable in all of its principal parts so that a wide variety of sizes and kinds of workpieces may be ground in the machine.

A still further object is to provide a novel grinding machine normally used for cylindrical grinding but also adaptable for grinding tapers by means of a plunge cut.

Other objects and advantages will become apparent from the following description. taken in connection with the accompanying drawings in which:

Figure 1 is a front elevational view of a machine embodying the features of the invention.

Fig.- 2 is a plan view of the machine. Fig. 3 is a fragmentary elevational view of the right end of the machine.

Fig. 4 is a fragmentary elevational view of the left end of the machine.

Fig. 5is a fragmentary sectional view taken on the line 5-4 of Fig. 2.

Fig. 6 is a diagrammatic view showing the relation between the grinding wheel and the work supporting means.

Fig. 7 is a fragmentary sectional view taken on the line 1-1 of Fig. 1.

Fig. 8 is an enlarged fragmentary sectional view I taken on the line 8-4 of Fig. 7.

- Fig. 9 is a fragmentary front elevational view,

partially in section, of the left-hand portion of the machine.

Fig. 10 is a fragmentary vertical sectional view taken on the line iiii 0 of Fig. 9.

Fig. 11 is an enlarged fragmentary front eleyational view/partially in section, of thecentral portion of the machine.

Fig. 18 is a vertical sectional view taken substantially on the line ll-Il of Fig. 11..

Fig. 14 is a fragmentary front elevationalview of the structure showninFig.13.

Fig.'l5 is a plan view of the structureshown inlig. 14. p

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Fig. 1.6 is a diagrammatic view showing the actuato and control valve for the work supporting mea s.

Fig. 1'7 is a sectional view of the valve taken on the line I l-l I of Fig. 16.

' Fig. 18 is a diagrammatic view showing the electrical and pressure fluid circuits of the machine.

Fig. 19 is a plan view, partially in section, showing a wheel dressing device for dressing the grinding wheel for cylindrical grinding.

Fig. 20 is a front elevational view partially in section showing the dressing device illustrated in Fig. 19.

Fig. 21 is a plan view of a wheel dressing device for dressing a grinding wheel for taper grinding.

Fig. 22 is a sectional view taken on the line 22-2-2 of Fig.21.

While the invention is susceptible of various modifications and alternative constructions, I have shown in the drawings and will herein describe in detail, the preferred embodiment,-but it is' to be understood that I do not thereby intend to limit the invention to the specific form disclosed, but intend to cover all modifications and alternative constructions falling within the spirit and scope of the invention as expressed in the appended claims.

General description of the machine A machine embodying the features of the invention comprises generally a base on which is mounted a grinding wheel and means for supporting a workpiece. The work supporting means preferably comprises a yoke swingable about an axis substantially parallel to the grinding wheel axis and arranged to support a workpiece on an axis which is also parallel to the grinding wheel axis but is eccentric to the axis of swinging of the yoke. Swinging movement of the yoke is controlled by a feed mechanism which acts on the yoke at a relatively great distance from the swinging axis, while the work is a relatively short distance from such swinging axis. Moreover, the work is so positioned that when it is moving toward the grinding wheel during the grinding operation, it moves at an angle to the peripheral surface of the wheel. Thus, because of such angular movement and the difference in the above-mentioned distances,

movement of the feeding means may be through a relatively great distance to produce a minute feed of the workpiece. feeding of the workpiece is therefore readily attained.

ng the grinding operation, the work is rotatably driven and also reciprocated axially, such reciprocation being held accurately in line with the axis of swinging movement by virtue ofthe fact that the yokeis both reciprocated andswung in the same bearings. If the reciprocation. were slightly out of line with the axis ofswinging, as might readily occur in the case where ways were provided for such reciproca- Accurate control of the impart a decreasing rate of feed to the yoke.

Thus as the work approaches its final ground diameter, such decrease in feed rate tends to produce greater accuracy in the final ground dimension. The reciprocation is constant during the entire grinding operation so that with a decreasing feed rate, the number of reciprocations per unit depth or feed increases, which results in a uniform diameter throughout the length of the ground portion of the work.

The various movements of the machine are coordinated by a control means which permits the machine to operate as an automatic machine to the extent that when a workpiece is put into the machine and initial movement instituted, the machine auomatically carries through its operations to the point where the workpiece is ready to be removed and a new one inserted, With such automatic operation, interlocks between the various parts of the machine are provided so that the various steps will take place only in-their proper sequence. Furthermore, in order to insure accuracy of grinding, the grinding wh'eel spindle and its support are so constructed that no distortion thereof will occur by overheating, and should any overheating occur, the machine will automatically stop.

As shown in the drawings, the machine comprises a base 80 which is elongated from left to right and is of generally L-shape (see Fig. 2) to provide a rearwardly extending portion Ii at the right side of the machine. On the rearwardlii extending portion Si is mounted a grinding wheel 32 which is driven by an electric motor 33.

Supported on the front portion of the base "1 a central U-shaped portion between the arms of which is supported a workpiece. At the ends of the arms of the U arealined bearing portions extending outwardly therefrom on an axis which parallels the front of the machine and is substantially parallel to the grindingwheel axis. The work supporting means in the arms or the U- shaped portion of the yoke hold the workpiece on an axis eccentric to the axis of swinging of the ycke and in such position that as the yoke is swung, the workpiece is moved toward the grinding wheel 32.

The swingins movement'of the yoke may be said to be divided into two portions, namely, a swinging movement through a relatively wide angle to move the yoke from a work loading position tion separate from the bearings for the swinging stead of being in the form of flat ways, and

' tion and the yoke thus provides a protecting to a grinding position, and then through a very much smaller angle to feed the work toward the grinding wheel. Preferably when the yoke is in work loading position, the arms of the U extend generally upwardly so that access to the space therebetween may be readily obtained at the front of the machine. To move the work into "grinding position the yoke is preferably swung forwardly so that the arms of the yoke extend horizontally forward during the grinding operaguard about the work at such time.

The workpieces are rotated during the grinding operation. To this end a work driving means, indicated generally at SI (see Figs. 1 and 2), is

mounted on one of the arms of the yoke 34 and has a drivingconnection with a portion of the thereof. The feed mechanism acts as a control means for the swinging movement of the yoke. while the, actual swinging of theyoke is effected by a means, indicated at 38, located at the back of the machine adjacent the left-hand end of the means ll thus swings the yoke between the work loading position and the grinding position and also during the feed for the grinding operation. However, the swinging movement during the grinding operation is controlled by the feed mech- The yokell is also reciprocated during the grinding operation. Such reciprocation, since the work is gradually fed toward the grinding wheel,

-is at a rate to provide a number of reciprocations during the feed. Since, as mentioned above, the

rate of feed gradually decreases toward the end Y yoke (see Figs. 2, 4, and 16). The yoke swinging of the feeding movement. and since the reciprocation is at a constant rate, the workpiece is uniformly ground throughout its length. Furthermore, as will hereinafter be described, there is a dwell of the yoke 34 at the end of the grinding operation for "sparking out" which insures uniformity of diameter throughout the length sinceth'e reciprocation of the yoke continues during such dwell.

For reciprocating the yoke,means is provided tending to move the yoke in one direction while a second means is provided for intermittently moving it in the opposite direction. Thus as shown in Figs. 1 and 2. the means constantly tending to move the yoke in one direction is located preferably at the right-hand end 01' the yoke and in the present instance comprises a fluid pressure actuator, indicated generally at 01. The actuator 31 tends to move the yoke to the left, as viewed in said figures. For intermittently moving the yoke to the right against the force exerted by the actuator 31, a power driven reciprocating means 40 (see Figs. 1, 2, 4, 9, and 10) is mounted on the left end of the base 30.

With the machine thus generally described; a brief general statement of the operation of the machine will facilitate the understanding of the more detailed description to be hereinafter given. Thus, assuming that the yoke 34 is in its idle or work loading position, that is, with its arms extending generally upwardly, a workpiece is loaded in the work supporting means between the arms of the yoke u. The yoke is then swung forwardly and downwardly by the yoke swinging means 36 to bring the arms of the yoke into a substantially horizontal position, by which movement the workpiece is moved into grinding position. Such swinging movement of the yoke also brings it into position to place it under the control of the.

feed mechanism 35 which operates to control the further swinging movement While the work is being ground. During the feeding movement, the reciprocating means 40 acts, in cooperation with the actuator 31, to effect reciprocation of the yoke to move the workpiece substantially parallel to the grinding wheel axis and thus grind the entire length 01' the portion of the workpiece to beground. Also during the feeding movement, the work is rotated by the work driving means 38.

- At the conclusion of the feeding movement there is a short dwell for the purpose of sparking out," and the yoke is then swung upwardly by the yokeswinging means it to permit removal of the workpiece and insertion of a new workpiece.

The foregoing cycle is initiated manuallyfbut The grinding wheel and its support As heretofore mentioned, the grinding wheel I! is supported by the rearwardly extending portion II of the base. It is so mounted that its axis extends substantially parallel to the front of the machine, with the wheel extending into the space between the arms of the yoke 34, as shown in Fig. 2. The grinding wheel is carried on one end of a spindle'BO (see Fig. 5) which is Journaled in a head II. The grinding wheel is of annular form and is mounted on a flanged member If rigidly secured to the left end of the spindle 50.

To. clamp the grinding wheel in place on the flanged member If, a clamping plate It 18 provided which is bolted to the flanged member II. On the opposite end of the spindle III a pulley 54 of the what type is secured and has a driving connection with the motor 33 which is positioned rearwardly of the grinding wheel.

Accuracy of grinding depends upon the accuracy with which the grinding wheel rotates. Because of the speedat which it is desirable to rotate a grinding wheel, there is a tendency for the wheel supporting spindle to heat up and thereby become distorted sufficiently to materially affect the accuracy of grinding. Moreover, the bearings which support a spindle subl ected to such heating cannot be made with a particularly tight fit because of the expansion or the spindle due to heating. Thus, inaccuracies of grinding occur between the time when the spindle is first started and is relatively cool, and the time when the spindle heats up.-

In the present instance the spindle is iournaled in the head II in such a manner that practically no material heating occurs. A very close fit between the bearings and the spindle may therefore be utilized. thus resulting in increased accuracy of grinding. To this end the head II is provided with spaced bearings 55 which are made of porous metal such as cintered bronze, or metal known in the trade as Oilite Bearing Bronze. Outside of the bearings annular wells Ii are provided to which oil is supplied under pressure by means of pipes 81. The oil inthe wells 56 is forced through the porous bearings 56 over the entire area thereof to lubricate the spindle. Since the oil is thus supplied to the spindle surface at a multitude of points throughout the entire area of the bearings, very little clearance need be provided between the bearings and the spindle, and the spindl is therefore held accurately positioned at all times. Furthermore, by supplying oil in this manner it is found that very little heating. of the spindle occurs. i v

The oil as it works along the spindle is collected in a central well so, or in end wells 0! which are connected to the central well 60 by drains 62. The oil collected in the central well 60 may then be carried back to the source of supply through a return pipe 63. Oil is supplied to the bearings 65, through the pipes 01 by means of an oil pump 68 driven by a motor 66 located in the lower right hand portion of the base, as shown in Fig. 1, the return pipe 63 being connected to a reservoir for the pump 68.

In addition to preventing the spindle from overheating by use of the porous bearings, the spindle is also water cooled. To this end it is provided with a central cavity 66 into which a pipe 65 extends, the pipe 66 also extending beyond the end of the spindle for connection to a source of water under pressure (not shown). The pipe 66 is of substantially smaller diameter than the interior of the cavity 66 to permit water entering the cavity by means of the pipe to flow through the cavity. To support the pipe, 2.

bushing 66 is secured to the spindle for rotation therewith as by being threaded into the outer end of the cavity 64. The bushing 86 at its outer or.right-hand end, as viewed in Fig. 5, fits snugly around the pipe to prevent leakage of water therefrom. The interior of the bushing 66 at its inner end is enlarged as at 61 to provide a space in communication with the central cavity 64. On the outer end of the bushing is mounted a collecting ring held against rotation relative to the bushing 66 and provided with an annular chamber M. The chamber 1| is in com munication with the enlarged interior 61 of the bushing by means of radial apertures 12 in the bushing. The annular chamber 1i is connected with a discharge pipe 13 to carry off the water after it has passed through the central cavity 66.

I Thus there is a constant flow of water through the interior of the spindle 50 to carry away what little heat'may be generated. I

The head BI is mounted on a table 14 (see Figs. 2 and 3) which is slidably mounted on the rearwardly extending portion 3| of the base for movement toward and from the workpiece so that the grinding wheel may be positioned for grinding workpieces of different diameters. To this end the rearwardly extending portion iii of the base is provided with ways 16 supporting the table 14. The table 14 is adapted to be adjusted on the ways 15 by means of a manually operable screw 16 carried-by the base of the machine and threaded into a nut 11 fixed in a lug 60 extending downwardly from the bottom of the table 16. The screw 16 extends forwardly through an intermediate wall ill (see Fig. 3) in the base and the front wall 82, and is held against endwise motion by thrust bearings. 83. The front end of the screw 16 is provided with a squared end 64 to receive a hand crank 85 by which the screw may be rotated to'eifect rough adjustment of the grinding wheel.

For fine adjustment of the grinding wheel, the screw 16 immediately inside of the front wall 82, carries a gear 86 of relatively large size meshing with a smaller idler gear 81 (see Fig. 1) carried on a stub shaft 90 mounted on the front wall 82. The idler gear 81 also meshes with a pinion 9i carried on a shaft 82 rotatably supported by and extending through the front wall 82. The front end of the shaft 02 is also squared to receive the hand crank 85 and is provided with a calibrated dial 03 and a relatively fixed indicator plate 84 to facilitate accurate setting, .of the grinding wheel.

In order to facilitate turning the screw 16' manually for rough adjustment of the grinding wheel and to avoid rotating the calibrated dial 63 at such times, the pinion 9| is mounted so that it may be shifted out of mesh with the idler gear 81. To this end the shaft 02 which carries the pinion 0i is eccentrically carried in a bushing mounted in the front wall 82. By rotating the bushing 66 in the front wall, the pinion 0i may thus be moved out of mesh with the idler gear 81. The eccentric bushing 95 likewise facilitates assembly of the structure since the shaft 82 is readily adjustable relative to the stub shaft 60 to take up backlash between the pinion and the idler gear.

The grinding wheel 32 is provided with a guard structure which is so constructed that it may be readily moved away from the wheel to facilitate replacement of the wheel when necessary. As shown in Figs. 2 and 5, the guard structure comprises a disk 96 mounted on a hub portion of the head 5| adjacent the inner face of the grinding wheel. Covering the periphery and the outer' face of the wheel is a dished structure 91 provided with peripherally spaced lugs I00 into which screws are inserted to secure the dished structure 81 t0 the disk 96. The dished structure 91 is carried by an arm IOI extending radially of the grinding wheel and pivotally supported on a vertically extending pin in carried by a bracket I03 rigidly secured to the table 14. By such pivotal support the dished structure 91 may be swung away-from the wheel to permit ready removal of. the wheel from its spindle. When the dished structure 81 is in place and secured to the disk 96, the arm IOI is rigidly secured against swinging movement by means of a screw I04 extending through the arm IOI and threaded into a lug I06 on the bracket I03.

The disk 96 and the dished structure 91 are cut away at their front lower portion, as shown at I06 in Fig. 3, to provide access for the workpieces to the grinding wheel. Carried by the peripheral portion of the dished structure 91 is a nozzle I01 for supplying coolant to the workpiece at the point of grinding. Preferably the nozzle is located at the forward or front edge of the cut away portion I06 of the guard structure.

It is of course desirable to hold the nozzle closely adjacent the work so that the coolant will be sup plied directly to the point of grinding. In grinding different diameters, it is therefore desirable to be able to adjust the nozzle so that it may be placed closely adjacent a workpiece of any size. In the present instance such adjustment is effected by rotatably adjusting the dished structure 91 on the arm IOI. To this end the dished structure 01 is provided with a hub IIO fitting in a round boss III on the end of the arm IOI. The hub H0 is rotatable in the boss III and is adapted to be rigidly clamped thereto by means of asci'ew H2. The guard structure may thus be rotatably ad" justed on the arm IM to place the nozzle I01 immediately adjacent the portion of the workpiece being ground. When the guard structure is moved away from the wheel for replacement of the latter, the nozzle I01 is likewise moved away since it is carried by the guard structure. Coolant is supplied to the nozzle I01 through a pipe extending from a pump I00 driven by a motor I09 located at the rear of the base 30, as shown in Figs. 2 and 4.

Work supporting structure I As heretofore mentioned, the work to be ground accuracy desired.

is supported by the yoke 24 which is swingable through a relatively large angle from a work loading position to a grindin position, and then by am II2. One of the centers is made longitudinally movable to permit insertion of a workpiece and to accommodate workpieces of diflerent length. To this end the center supporting member I24 is slidable longitudinally relative to the yoke. For such longitudinal movement, the center supporting member I24 is permitted to slide wheel entering such space to contact the work.

Extending outwardly from the ends of the arms in the bushin I22 and also has a reduced end portion I22 slidable in a bushing I21 in the yoke. To move the center longitudinally, the supporting member I24 isprovided with rack teeth I 22 on its lower face meshing with teeth I 22 cut on a II 2 are bearing portions II2 rotatably journaled in bearings II2 mounted on the base of the machine to support the yoke for its swinging movement.

The yoke is reciprocated, as mentioned above,

during the grinding operation to insure that the entire length of the part being ground is ground to a uniform diameter. If'the yoke were mounted for such reciprocation on ways which were separate from the bearings II2, any misalinement between such ways and the bearings would cause the work to be ground with a taper. Moreover, such ways are usually in the form of longitudinally extending flat surfaces which require very accurate hand scraping. With such a construction it would therefore be difficult to obtain the The manner in which the yoke 24 is mounted both for its reciprocation and its swinging move. ment eliminates any chance of obtaining an undesired -taper on.the-workpiece and furthermore avoids the difliculties ofhand scraping, To this end the bearings II2 which support the yoke for.

its swinging movement also serve to support the yoke for its reciprocating movement. Thus the bearing portions I I2 are made considerably longer than the bearings I I2 so that the bearing portions Ill may move longitudinally in the bearings H2 andmay also rotate therein.

To avoid exposing any part of the bearing portions to dust or Brit in the grinding operation, covering means are provided on both sides of each bearing 2 to protect the parts of the bearing portions II2 which project therebeyond. On the inner side of each bearing I I2, or the side nearest the U-shaped portion of the yoke, the covering means extends from the bearing III to the arm I I2 and is collapsible to provide for the reciproca' tion of the yoke. Thus cover members II1 are provided which are in the form of bellows, each of which is attached at one end to the bearing H2 and is provided with a ring I22 at the other end held against the arm III. The cover member H1 is of flexible material, such as heavy canvas, and includes a coiled spring secured to the canvas which tends to expand and hold the ring I22 in contact with the arm H2. Thus, with the reciprocation of the yoke, the cover members II 1 are alternately collapsed and expanded.

The outer ends of the bearing portions III are,

likewise covered. For this purpose the right-hand bearing H2 is provided with a cup-shaped cover I2I secured to the bearing H2 and. of sumcient length to permit the reciprocation. of the bearing portion II 2 therein. At the outer end of the lefthand bearing I I2 is a cylindrical cover I22 secured to the bearing I I2.

As mentioned above, the workpiece is supported in the space between the arms II2 on centers to permit rotation of the work during grinding.

The right-hand center, indicated at I22 (see Figs. '1 and 8), is mounted in a center supporting member I24 carried in a bushing I 22 in the right-hand manually operated shaft I2I extending transversely to the axis of the center I22. The shaft I2! .is iournaled in the right-hand arm H2 of the yoke and has a portion projecting forwardly therefrom, on which is mounted a handwheel I22 for rotating the shaft. Thus, rotation of the shaft I2I moves the center I22 longitudinally to permit insertion and removal of the work. To lock the center in any adjusted position, suitable locking means, indicated at I 22, is provided for the haft I2I. Y

The center I22 is also laterally adjustable so that it may be accurately alined with the opposite center. To this end the bushing I22 ilts loosely in the arm H2 and four radially extendins set screws III are threaded into the arm II2 to hold the bushing I22 in its adjusted position. r

The left-hand center, indicated at I24, is mounted in a center supporting member I22 rigidly secured in a bore in the left-hand arm "2 as by a screw I22. The work is rotatable on the centers I22 and I24 and is driven during the grinding operation. To this end a pulley I21 is rotatably mounted on the center supporting member I22, suitable antifriction bearings I42 being provided therebetween. The pulley I21 is adapted to be connected to the work for driving the latter by means such as a dog I, similar to a. lathe dog, clamped on the adjacent end of the workpiece. To drive the pulley I21, the driving means 22 is provided which is preferably mounted on the adjacent arm ill of the yoke. In the present instance the driving means comprises a reduction gearing enclosed in a housing I42 (see Figs. 2 and 3) and driven by a motor I42 mounted on the side face of the arm H2. The reduction gearing has a pulley I44 connected to the pulley I21 by a belt I42. The housing I4 2-is pivotally supported on the arm H2 7 so that it may be shifted to provide a take up fluid. The actuator comprises a plurality of cylinders I42 provided with a common lower head I41 and a common upper head I22. The pistons within the cylinders I42 are all connected to a common cross bar III which in turn is connected to the yoke.

The connection to the yoke comprises a rod I22 pivotally attached to the free end of a lever arm I22 extending from a collar I24 mounted on the left end of the yoke 24. The collar I24 is connected to the yoke to swing it, but since the yoke is reciprocated, the connection between the collar and the yoke is arranged for such reciprocation. For this purpose the end of the yoke is provided with a reduced portion I22 to ll which is keyed a cup-shaped member I56 provided with splines I51 on its external surface for connection with the collar I54. The yoke may thus be swung by its actuator but is permitted to reciprocate relative thereto. To hold the collar I54 against endwise movement, the cylindrical cover I22 for the adjacent end of the bearing portion I I extends into abutment with the collar I54. On the outer face of the collar I54 is mounted a sleeve member I60 which forms a further protection for the end of the yoke.

Since the end of the lever arm I53, to which the rod I52 is attached, swings in an arc, the actuator I46 is swingably supported. To this end the lower head I41 of the actuator is provided with a pair of spaced ears I6I straddling a bracket I62 secured to the rear face of the left-hand end of the base 30, the ears I6I being pivotally connected with the bracket I62 by means of a pivot pin I63. In order to facilitate assembly of the machine, and particularly to locate the range of swinging movement of the yoke in the proper position, the bracket I62 is attached to the base 80 in such a manner that it may be adjusted vertically through a short distance.

While the machine is principally used for grinding cylindrical workpieces, it is also constructed so that it may be used for grinding tapers by means of a so-called plunge cut. For such grinding the yoke is moved so that its axis is out of parallelism with the grinding wheel axis. To provide for adjustment of the yoke to such position, the yoke supporting bearings II6 are mounted on a sub-base I58 (see Figs. 1 and 2) carried on the upper face of the main base 60. The sub-base I58 is shiftable on the main base about a vertical axis located midway between the arms of the yoke, a pivot pin I59 being provided for such shifting movement. To hold the sub-base I58 in any adjusted position arcuate slots I68 are provided adjacent the ends of the sub-base and clamping screws I69 extend through said slots and into the main base for clamping the sub-base in place.

When the sub-base is adjusted by the foregoing means so that the yoke axis is out of parallel with the grinding wheel axis, reciprocation of the yoke is stopped and feeding movement of the yoke toward the grinding wheel will cause the work to be ground with a taper. For such taper grinding the grinding wheel is preferably dressed to a true cylinder and is not tapered.

Reciprocation of the yoke Reciprocation of the work occurs throughout the grinding period and during the subsequent dwell to insure uniform grinding throughout the length of that portion of the workpiece to be ground. The reciprocation is not merely one stroke, as it would be in the case of a feed axially of the workpiece, but is a plurality of strokes during the grinding operation and at least one complete stroke back and forth during the dwell period at the conclusion of the feed so that "sparking out" will occur throughout the entire length of the part being ground.

The reciprocatingmechanism includes means exerting a constant force on one end of the yoke to urge it in one direction and actuating means at the other end of the yoke periodically moving the yoke in the opposite direction. The means exerting a constant force against one end of the yoke in the present instance acts'on the right end of the yoke and preferably utilizes fluid pressure. particularly pneumatic pressure, to exert the constant force. To this end the outer end of the right-hand bearing portion H5 is bored out to receive a cylinder I64 (see Fig. 1) which is flanged at its outer end and rigidly secured to the end face of the yoke. Extending into the cylinder I66 is a piston I65 fixed in a bracket I66 extending upwardly from the base 30, packing I61 being provided around the piston to prevent leakage. The piston I65 is provided with a central longitudinally extending passage I10 opening at its inner end into the interior of the cylinder I64 and connected at its outer end by means of a pipe I" to a source of air under pressure (not shown). Since the piston I65 is fixed by means of the bracket I66, pressure in the cylinder I64 exerts a force constantly urging the yoke to the left. To provide for the swinging movement of the yoke. the piston I65 is coaxial with the bearing portions II5 of the yoke.

The means for intermittently moving the yoke in the opposite direction, here indicated at 40, is located at the left end of the yoke and includes a power driven eccentric acting on the yoke.

, As shown in the drawings, said means comprises a carriage I12 (see Figs. 2, 4, 9, and 10) carried on the left-hand end of the base 60. The carriage I12 is provided with a housing I18 containing reduction gearing driven by a motor I14 attached to the rear face of the housing I16. The reduction gearing in the housing I16 includes a drive shaft I15 projecting horizontally forward from the front end.

On the drive shaft I15 is mounted the eccentric means for intermittently moving the yoke to the right. Since different workpieces may have parts of different length to be ground, it is desirable to be able to adjust the extent of reciprocation. Thus, the eccentric means comprises a tapered member I16 keyed on the projecting end of the shaft I15. Mounted on the tapered member I16 is an inner eccentric I11. The inner eccentric is clamped to the tapered member I16 by means of a screw I80 threaded into the end of ,the shaft I15. The screw I80 extends forwardly through a hub I6I on the inner eccentric and into a socket portion I82 on the front end of the hub I8I. end of the screw I60 as by a pin is a head I 63 turnably mounted in the socket portion I82 and having a squared end I84 extending forwardly of the socket portion I82. The screw may thus be turned by means of a wrench placed on the squared end I64. When the screw I80 is threaded into the shaft I15, the inner eccentric I11 is clamped onto the tapered member I16 by means of the head I86 bearing against the inner end face of the socket portion I62. When the screw is loosened, the inner eccentric I11 may be rotated about the tapered member I16, the hub portion I62 being externally hexagonal in shape eccentric I65 is normally clamped to the inner eccentric I11 but may be readily adjusted thereon to vary the aggregate eccentricity of the two eccentrics. on the hub I8I of the inner eccentric which gear is concentric with the periphery of the inner eccentric. Also mounted on the hub I6I is a clamping plate I61, the gear I66 and the clamp- Secured to the front To this end a gear I66 is mounted the two eccentrics. To adjust the outer eccentric.

an aperture I92 is provided in the outer eccentric to removably receive the endof a manually operated shaft I99. The shaft I99 carries a pinion I94 adapted to mesh with the gear I98 so that by rotating the pinion I94 the outer eccentric I85 is turned on the periphery of the inner eccentric I". When the outer eccentric has been adjusted to the point desired, the screws I99 holding the gear I86 in place are tightened, causing the outer eccentric I85 to be clamped between'the gear I99 and a flange I95 provided on the rear part of the inner eccentric I'I'I.

The aggregate eccentricity of the two eccentrics depends upon the direction of the outer eccentric relative to the inner eccentric. Preferably the individual eccentricities of the two eccentrics are equal. Thu-s when the inner eccentric is adjusted relative to the tapered member I19 to place its eccentricity in one direction, and the outer eccentric is adjusted relative to the inner eccentric to place its eccentricity in the opposite direction, the aggregate eccentricity is zero. When the eccentricities of the two eccentrics are in the same direction, the aggregate eccentricity of the two is double the value of either one. It is obvious therefore that any amount of eccentricity may be obtained between zero and double the eccentricity of either of the eccentrics merely by suitable adjustment of the two eccentrics.

The outer eccentric acts on the yoke to force it to the right against the pressure exerted by the actuator 31. To insure smooth operation, the cup-shaped member I56 on the left endof the yoke is provided with a bracket I96 (see Figs. 1 and '7) carrying a roller I9! bearing against the-periphery of the outer eccentric I95. The

roller I91 is positioned substantially in the plane' ofthe outer eccentric I85 when the yoke is in grinding position. When the yoke is turned to th .-,workvloading position, obviously the plane of the roller I9! is transverse to the plane of the outer eccentric I95. However, atsuch' time, the eccentric is not being driven.

In addition to providing for adjustment of the extent of reciprocation. the reciprocating means 40 is also adjustableto vary the position of such reciprocation. Thus, on certain workpieces portions at opposite ends of the workpiece may have to be ground. Obviously it is desirable to reciprocate the work relative to the grinding wheel only to the extent that is necessary to insure complete grinding of the particular portion being suit workpieces of different character. To this end the gearing in the housing I19 may be of the variable speed type or, if preferred, the motor I 14 which drives the reciprocating means.

.may be of the variable speed type. Thus the yoke tends to urge the eccentric means to suchv position and to.-oppose any movement beyond such point. Thus the yoke is in its extreme left hand position when swung to the work loading position.

Feed mechanism As mentioned heretofore, the yoke 94 swings the work from a work loading position to a grinding position, and during the grinding operation the feed mechanism, which-has been indicated generally at 35, controls the swinging movement of the yoke. The feed mechanism includes a feed plate 2| 0 (see Figs. 11 and 13) movable in a controlled manner and provided with an abutment for the yoke so as to control the movement thereof in accordance with the movement of the feed plate 2I9.

One of the principal features of the feed mechanism lies in the fact that it may move through a relatively great distance to effect a small movement of the workpiece toward the grinding wheel. Thus the actual feeding movement oi. the work is readily controlled. In order to permit of such relatively large movement of the feedingplate, the intermediate portion Ill-of the yoke is the part which is controlled by the feed plate, and since the intermediate portion II 4 is at a relatively great distance from the axis'oi' swinging of the yoke, the desiredextent of movement is obtained, To provide for the abutment between the yoke and the feed plate 2), a downwardly extendinglug 2I I is provided on the intermediate portion III of the yoke, and into the. lower face of the lug 2II is secured a hardened ball 2I2. The lug on either side of the ball 2I2 is beveled, as at '2I3, the beveledsurfaces being provided with wear plates 2 I4.

The feed plate 2I0 is movable vertically, and since the yoke is reciprocated horizontally during grinding, means is provided to permit of such reciprocation of the yoke while the feed plate moves downwardly. To thisend the top edge,

indicated at 2 I5, of the feed plate constitutes ways for a slide 2I8 mounted thereon. The slide 2I6 has a channel shaped form straddling the top portion of the feed plate and slidable on the top edge or ways I. To hold the slide 2I9 on'the feed plate, a groove 2" is cut in the front face of the plate parallel to the top edge 2II, and a pair of pins 220 extend from the slide 2I6 into 203. Threaded into the nut is a screw 29 rotatably mounted in the table "I but held against endwise movement therein. 'On the outer end of the screw is a handwheel flii for rotating the screw, and a dial 208 may be provided to facilitate setting of the position of the carriage III.

The rate of reciprocation may also be varied to the groove 2". The upper face of the slide 2I6 is provided with a transversely extending V- shaped notch 22I to receive the wear plates 2 on the beveled surfaces of the lug 2| I. By this construction when the yoke is lowered into contact with the slide 2I9, the beveled surfaces and the V-shaped notch cause the lug 2 to be centered within the notch. At the bottom of the r V-shaped notch is a hardened anvil 222 serving as a bearing surface for the ball 212.

The yoke when it is in its raised or work loading position is out of contact (with the slide 218. However, upon lowering or swinging the yoke forwardly to the grinding position, the ball 212 contacts the anvil 222 on the slide 216 and further swinging movement of the yoke is'thus placed under control of the feed plate 212.

The feed plate 2111 comprises a wide portion at the top so that the top edge 21! is of sufilclent length to rovide for the reciprocation of the slide 216. The lower portion of the feed plate 210 is preferably of reduced width, such reduced width permitting ready access to other parts of the mechanism located behind the feed plate. The feed plate must be guided so that its top edge 215 is at all times held parallel to the axis of swinging of the yoke when cylindrical workpieces are being ground. This is necessary in order to avoid grinding the workpiece on a taper since if the top edge 215 of the feed plate were slightly out of parallel relative to the axis of swinging of the yoke, the reciprocation of the' yoke would cause the work to be ground on a taper. The feed plate 210 is therefore accurately guided by means secured to the base of the machine. As shown herein, the guide means comprises a pair of guide rollers 222 mounted at opposite sides of the upper wide portion of the feed plate and a pair of guide rollers 224 mounted at opposite sides of the lower portion of reduced width, all four guide rollers being rotatably mounted on brackets 225 secured to the front face of the base of the machine.

The feed plate 211! is moved slowly or gradually in order to effect the proper feeding movement of the work toward the grinding wheel. Such movement of the feed plate is adjustable in a number of ways in order that it may be readily adapted for workpieces of different sizes. One of the prominent features of the machine lies end of the cam member 221 is supported by I. shiftable member 235. The member 222 is provided with a slanting surface 226 on which the free end of the cam member 228 rests, and is adjustable longitudinally of the rod 221 to raise or lower the free end of the cam member 222. For this purpose the shiftable member 222 is provided with an elongated slot 231 through which a bolt 240 extends to lock the shiftable member 235 to the rod 221 in its adjusted position. Thus by adjusting the shiftable member 225 the angle of the cam surface 230 may be changed to vary the extent or range of movement of the feed plate.

The rod 221, as referred to above, is shiftable horizontally to effect the movement of the feed plate, and its movement is such as to provide a decreasing rate of feed. For this purpose the right-hand end of the rod 221 constitutes a piston 241 operating in a cylinder 242, and fluid pressure, in the present instance'pneumatic pressure, is supplied to the cylinderto effect such movement of the rod. Thus pneumatic pressure may be supplied to the end of the cylinder 242 through a pipe 243.

The movement of the rod 221 to the left under the pressure exerted in the cylinder 242 is controlled to provide a slow feeding movement of decreasing rate. To this end the left-hand end .of the rod 221 also constitutes a piston 244 operating in a cylinder 245. The cylinder 24! is adapted to be filled with oil drawn from a reservoir 24B, and the slowness of movement is obtained by causing the oil to be forced through a restricted orifice. Thus, oil is forced from the cylinder 245 through an opening 241 in the end thereof into a chamber 248. The upper end of the chamber 248 is closed by a plug 249 provided with the above-mentioned restricted orifice, here indicated at 250. In order to provide adjustment for the rate of feed, the flow through the restricted orifice 2511 maybe adin the fact that the rate of feeding movement of the workpiece relative to the grinding wheel gradually decreases during the grinding operation. The advantage of this is that the final grinding in the grinding operation is very light, resulting in great accuracy of the finished workpiece.

To accomplish this end, means is provided for effecting the movement of the feed plate which embodies structure attaining these advantageous features. As shown in the drawings, the vertical movement of the feed plate is controlled by a cam member 226 (see Fig. 11) carried on a rod 221 movable transversely of the direction of movement of the feed plate, or, in the present instance, horizontally. The cam member 226 is provided with aslanting cam surface 2311 contacted by an abutment 231 on the feed plate. With the cam surface 230 positioned as shown in Fig. 11, movement of the rod 221 to the left lowers the feed plate 210. In order to permit adjustment of the position of the movement of the feed plate, the abutment 221 is in the form of an eccentric mounted on a stud 222 and adapted to be locked in place by a nut 222 threaded on the end of the stud. Rotation of the eccentric abutment 231 about the stud 222 thus will raise or lower the feed plate 2111 relative to the cam surface 220 to justed by means of a needle valve 251. The oil flowing through the orifice is conducted to the reservoir 246 by means of a short pipe 222. When the piston 244 moves to the right, oil is returned to the cylinder 245 through a passage 252 controlled by a ball check valve 254, the oil thus being permitted to flow freely into the chamber 248 and back into the cylinder through the opening 241.

While the fluid pressure in the cylinder 242 eflects movement of the rod 221 to the left to lower the feed plate 210, movement of the rod 221 to the right to raise the feed .plate after the grinding operation and in preparation for another workpiece, is effected by spring means. As shown herein, said spring means comprises a coiled spring 2611 located in the cylinder 245 and abutting at one end against the end wall of the cylinder. At the other end the spring 280 is positioned in a bore 261 in the end of the piston 244. Thus when the rod 221 is moved to the left by the pressure fluid in the cylinder 242, the spring is compressed. After the grinding operation the pressure fluid in the cylinder 242 is released and the spring 2611 moves the rod to 21.1: right and consequently lifts the feed plate The decreasing rate of feed is attained by the structure just described. The pressure exerted on the piston 241 in the cylinder 242 is constant. Such constant pressure, neglecting for the moment the counter pressure exerted by the spring 262, would produce a constant flow of oil through the restricted orifice 250, and .a consequent conmovement of the feed plate.

nected to a valve 2" located on movement of the portion of the pressure exerted by the pressure fiuid in the cylinder 242, which is available to force oil through the restricted orifice 288, decreases. The flow through the restricted orifice 288 therefore decreases, since fiow through an orifice is proportional to the pressure, and the rate of movement of the rod 221 to the left thus decreases. i Since the rate of movement of the rod to the left decreases, the actual feeding movement of the work toward the grinding wheel as a result thereof decreases. Buch decrease in feed rate is substantial since, it will be noted from Fig. 11, the spring 288 is materially compressed in length during the movement 'of the rod 221 to the left so that a substantial increase in' counter pressure by the spring 288 occurs.

The movement of the feed plate 2L8 is limited. and to this end a positive stop 282 is provided.

' I" by a Pi 212.

The lower end of the reduced portion of the feed plate 2H1 is provided with a finger 288 adapted to abut the stop 282 and thus limit the downward since the extent or range of movement of the feed plate is ad- Justable by means of adjusting the cam surface 220, the positive stop 282 is similarly adjustable so that for any point of adjustment forthe cam surface 288 the positive stop 282 may be utilized. For this purpose the peripheral surface of the positive stop 282 is in the form of a spiral, and the stop is carried bracket 288 (see Figs. 11 and 12) on the base of the machine. 011 the front end of shaft 284 is an arm 288 provided with a handle for rotating the shaft 284 and the stop 282. To facilitate setting the stop in any desired position, the arm 288 is also provided with a pointer 288 cooperating with indicia provided on an arcuately shaped plate 281 fixed to the base of the machine (see' Figs. 1 and 12). The arm 288 is held in any position to which it is adjusted by means of a leaf spring 288 secured to the arm and frictionally bearing against the rear face of vthe arcuate plate 281.

Controlsjor the machine One of the principal features of the machine has in the provision of controls whereby the machine may be started through a manual control and thereafter automatically performs the grinding cycle and returns all parts to a position ready for another cycle. The controls utilized for operation of this character are of such construction that interlocks are provided so that the various movements in the machine will take place in the proper sequence. Such controls are best understood by consideration of the diagram of Fig. 18, which shows the interconnection of the various control members in relation to the principal parts of the machine. However, before describing the various circuits involved in such controls, the apparatus utilized will first be descri As heretofore mentioned, theyoke 84 is swung from a work loading position to a grinding position by the swinging means or actuator 88. The actuator 88 being pneumatic, air under pressure is supplied alternately to the upper and lower heads I88 and I41 to swing the yoke from one position to another. The upper head I88 has a pipe 218 (see Figs. 2, 4', 13, 14, 18, and 1'1) conona shaft 284 mounted in a one end of the passage 18 machine adJacent the feed mechanism. The lower head 141 is likewise connected to the valve The valve'21i may be of any desired form but preferably comprises a cupshaped casing 218 in which a valve member 214 is rotatably mounted, the valve member being secured in the casing by a cover 218 which also serves as a bearing for a stem 218 valve member. The valve member wise provided with a stem 218 on its opposite end projecting outwardly beyond the. casing.

The pipe 218 from the upper head of the ac- 214 is likesource of pneumatic pressure (not shown), the

pipe 2" being in communication passage 282 which of the valve member 214. tion of the valve member the passage 282 con-. nects with a diametric passage 288 which is bowed so that its respective ends may communicate with the two passages 211 and 288 when the valve member is properly turned, and will provide space for another passage hereinafter described. Thus when the valve member 214 is turned so that 288 is in commurication with, for example, the passage 211 connected with the upper end of the actuator, pneumatic pressure will be supplied to said end through the passages 288 and 211 and the pipe 218. The other end of the diametricpassage 282 will be blanked oh by the c m! 211. Such position is clearly shown in Fig. 11. By rotating the valve member 214 through 90,, iii a counterclockwise direction as shown in Fig/ 17, the left-hand end of the diametric passage 282 will be turned to communicate with the passage 288 and the lower end of the actuator 88. Thus by rotating the valve member 214 through 90", pneumatic pressure from the supply pipe 281' may be selectively supplied to either end of the actuator 88 to move with a central the piston therein in opposite directions.

' pressure is supplied to one When pneumatic end of the actuator, it is of course necessary to release the pressure in the opposite end. For this purpose, the stem 218 of the valve member 214 is the front of the Thus the piston in the tation that is provided with a central longitudinally extending passage 284 which at the outer end of the stem 218 vents to the outside atmosphere. Within thevalve member proper the passa e 284 stops short or the passage 282 so as to be separate therefrom and-is provided with a radially extending portion 288 adapted to be placed in communication with the passages 211 and 288 alternately by rotation of the valvemember 214. The radially extending portion 288 is positioned at right angles to-the diametric' passage 288 so that when the latter is connected with one of the iongitudinal passages 211 or 288, the radial portion 288 will be in communication with the other and will be turned from one to the other with the ronecessary to turn the .diametric passage 288 from one to the other.

It will be apparent from the foregoing description of the valve that when pneumatic pressure is connected to one end of the actuator 88, the other end will be relieved of pressure ,by exhausting through the passage 284 in the stem 218 of the valve, and that this condition may be reversed. actuator may be forced on the rotatable leads into the main portion Within the main por through 90",

while reverse movement of the actuator moves the yoke back from the grinding position to the work loading position.

. Mounted on the front end of the valve stem 219 is a hand crank 299 (see Figs; 13. 14. and 19) having its hub portion keyed to the stem 2'". Thus the valve member may be rotated manually to properly position the passages therein. Also mounted on the valve stem 219 is a means for automatically rotating the valve member 219 at the conclusion of the grinding operation to cause the actuator to swing the yoke back to the work loading position. As shown herein said means comprises a valve lever 29! having a portion of its hub cut away, as at 299. The cut away portion 299 extends for somewhat more than 90 to receive a lug 29i on the hub of the hand crank 299.

To explain the operation oi the foregoing parts, .when the hand crank 299 is turned clockwise to the position shown in Fig. 14, the valve lever 29! is likewise moved to the corresponding position shown in that figure by engagement of the lug 29l with valve lever 291. Movement of the valve lever 29'! counterclockwise through 90 by means hereinafter described will result in moving the hand crank 299 back to its original position, the valve lever 29! contacting the lug 29l to effectsuch movement. Should it be desired to swing the yoke back to the work loading position at any time before the completion of the grinding operation, the hand crank 999 may be manually turned counterclockwise. through 90 without effecting any movement of the valve lever 29! since the cut away portion 299 of the valve lever permits the lug 29l to be so .moved. However. in normal operation of the 'machine, the hand crank 299 is utilized to move the valve member 219 in a clockwise direction to swing the yoke from a work loading position to a grinding position. and the valve lever 291 is moved in a counterclockwise direction to so move the valve member 219 and thus cause the yoke to be swung from its grinding position back to its work loading position.

Movement of the valve lever 29'! is effected by means of a tension spring 292 (see Figs.,-13, 14, ;and connected at its upper end to the free end -of the valve lever and anchored at its lower end .to' a'flxed part of the machine. The spring ob- =violisly will be tensioned at the time the hand crank 299 is turned to the position shown in Fig. 14. To prevent the spring 292 from acting immediatelyafter the hand is removed from the hand crank 299. a bar 299 is also connected to the 'free end of the valve lever 28?, the lower end of the bar being suitably guided as hereinafter described.

notch 294 adapted to receive a horizontally acting locking member 299. The notch 299 and the locking member 299 are so positioned that when they are engaged, the valve lever 291 will be held in the position shown in Fig. 14. The lockin member .299 is carried on a slide 299, the latter ,being urgedin a direction to cause engagement of the locking member 299 and the notch 294 by a tension spring 291. The spring 29'Ithus tends .to move the locking member 299 to its notch engaging position and will do so when the valve lever is turned to the position shown in Fig. 14,

Intermediate the ends of the bar is a 1 which results in causing the yoke grinding position. Release of the to'move to the lock m may be eiiected by means of a bell crank 999 pivotedon a fixed partof the machine and having one arm connected to the slide 299. The other arm of the bell crank 999 is connected by a link "I to the armature of a solenoid 992. Thus when the solenoid is energized, the armature thereof/will be Pulled downwardiy as shown in Fig. 14 to release the lock 299. Release of the lock 299 permits the spring 292 to turn the valve lever 291 counterclockwise and thus cause the air pressure in the actuator 99 to swing the yoke to the work loading position.

Since the swinging of the yoke back to the'work loading position is to take place after the completion ofthe grinding operation, the solenoid 992 is adapted to be energized at such time. The completion of the grinding operation occurs when the finger 299 on the feed plate 2l9 contacts the positive stop 292. Therefore simultaneously with such contact between the finger and the positive stop, the solenoid 992 is adapted to be energized. To this end the circuit for the solenoid is controlled by a micro switch 999 (see Figs. 11 and 18) mounted on the lower portion of the feed plate 2l9 adjacent the finger 299.. The micro switch 999 is so positioned that its actuating member will contact the positive stop 262 .and be actuated thereby at the same time that the finger 299 contacts the stop. The positive step 292 is thus made long enough :ghe contacted not only by the finger but also by e actuating member of the micro switch 999. The micro switch 999 is of the normally open type so that when its actuating member is actuated by contact with the positive stop, the circuit for the solenoid 992 will be closed to effect release of the lock 299, and consequent release of the bar 299 so that the spring 292 may turn the valve lever 291. F

As heretofore mentioned, at the conclusion of the feeding movement a. dwell is provided for sparking'out." Such dwell or delay should be long enough to permit the yoke to complete at least one reciprocation during the dwell period. Means is therefore provided to slow down the action of the spring 292 in turning the valve lever 291 so that the time required for the valve to be rotated through its movement and to the position forefiecting the return swing of the yoke will provide the necessary dwell period. For this purpose the lower end of the bar 299 is connected to a dash-pot structure which slows down the turning movement of the valve lever 291. The dash-pot structure comprises a cylinder 999 in which is mounted a piston 999 connected to the lower end of the bar 299 (see Figs. 13-and 14). The cylinder 999 comprises a part of a casting which also includes an oil reservoir 999. Downward movement of the piston 999 caused by the tension spring 292 forces oil from the cylinder 999 through an adjustable needle valve 99'! located in the base of the cylinder casting. and thence through a passage 9l9 into the lower end of the reservoir 999. A sufllcient quantity of oil is provided so that as the piston 999 moves downwardly, oil in the reservoir 999 will overflow from the reservoir into the top of the cylinder 999, a passage 999 through the intervening well being provided for this purpose. The needle valve 991 is adjustable by means of a knob 9H and the opening of the valve is adjusted to cause the time required for the piston 999 to force the oil out of the cylinder 999 to equal the desired dwell period. Obviously with this construction the dwell period 

